Re: [PATCH 1/2] clk: mvebu: armada-37xx-periph: Fix switching CPU rate from 300Mhz to 1.2GHz

Stephen Boyd
2018-07-09T16:44:49Z

Quoting Gregory CLEMENT (2018-07-09 08:42:31)
> Hi Stephen,
>
> On ven., juil. 06 2018, Stephen Boyd <sboyd@kernel.org> wrote:
>
> > Quoting Gregory CLEMENT (2018-06-29 07:44:02)
> >> Hi,
> >>
> >> On mar., juin 19 2018, Gregory CLEMENT <gregory.clement@bootlin.com> wrote:
> >>
> >> > Switching the CPU from the L2 or L3 frequencies (300 and 200 Mhz
> >> > respectively) to L0 frequency (1.2 Ghz) requires a significant amount
> >> > of time to let VDD stabilize to the appropriate voltage. This amount of
> >> > time is large enough that it cannot be covered by the hardware
> >> > countdown register. Due to this, the CPU might start operating at L0
> >> > before the voltage is stabilized, leading to CPU stalls.
> >> >
> >> > To work around this problem, we prevent switching directly from the
> >> > L2/L3 frequencies to the L0 frequency, and instead switch to the L1
> >> > frequency in-between. The sequence therefore becomes:
> >> >
> >> > 1. First switch from L2/L3(200/300MHz) to L1(600MHZ)
> >> > 2. Sleep 20ms for stabling VDD voltage
> >> > 3. Then switch from L1(600MHZ) to L0(1200Mhz).
> >>
> >> Do you have any comment on this fix?
> >>
> >
> > Looks good. Is it crashing right now? I can throw it into clk-fixes if
> > it's fixing pain.
>
> Yes for the SoC capable to run at 1200Mhz it crashes. At the time the
> initial support was provided, my SoC version only ran at 1000MHz, so the
> problem was not noticed.
>

Ok. Applied to clk-fixes.